Pyridine extraction process



sept. 23, 195s J. J. MooN PYRIDINE ExTRAcTioN PReCEss Filed Dec. 28. 1955 mm Kam INVENTOR. J J MOON BY M A7`7"ORNEV$ Wl, mm2;

United States Patent O PYRIDINE EXTRACTION PROCESS.

John J. Moon, Bartlesville, Okla., assignor to Phillips Petroleum Company, a corporation of Delaware.

Application December 28, 1953, Serial No. 400,612.

7 Claims.' (Cl. 260--290) The present invention'relates'.toI the separation .of -individual organic nitrogen bases from an aqueousmixture thereof.: More specilically,` it relates-'tothe separation and:.recoveryV oftwo or moreheterocyclic. nitrogen compounds. froman vaqueous solution' thereof by solvent extra'ctionz,

This. inventionfis particular-ly'suited for the separation ofclose-'boiling heterocyclic 'nitrogen bases; e. g., the separationz'r of z' 2rr1ethyl5vinyl` pyridiney (MVP) from 2- methyl-.S-ethyl ,pyridine (MEP), a difficult voperationv by conventional..separation methods.r If these" two compounds-aree separated byA thermal distillation, .considerable polymerization; of M-VP? results, since- MVP' polymerizes totan .appreciable f degree i .at 'elevated temperatures. The separation:vv can-.bermade s by 'vacuum-'steam distillation at lowertemperatures, butf this method' hasxthe disadvantage of: '.requiringt a Avery largezlcolumn .with 'a relatively*` high operatingfzcostm Solvent: extraction' was f investigatediias possible; low cost'- methodrlfor' the.' separation of 'these' pyridines; Aqueous acidso1vents,:aqueous .aminezsolventa yand aqueousgglycolvsolvents Nvere considered in 'surveying the field ofselectivesolvents. Most of theseiwere-tfo'und to'thave: one or rmorez serious; disadvantagessuchl as high cost, low selectivity, low solubility; high polymer 'acceleration, diiiicultseparationibetweensolvent and pyridine; andi` highly f corrosive fnatnre. While f'acids; 1 `for L'example,i are good solvents fo-rpyridinecompoundsandfcan'beiused to separate close-.boilingandV structunally'fsimilar:compounds, it: vis fdiicult to recover! :the pyridine .from most acids. Oridinar-ily, this `requires at least partiallyneutralizing the acid, which. is- .expensive f and; generally impossiblei in large scale :operat-ions. AmoreV signicantobje'ctonrtoitheuse of/ acidsl is theirV tendency j to .promote-1a polymerization :ofv py-ridines;

An; exception .to the-,.-generalzrnn of acidslis -alsolution of CO2 in. water :or carbonio-acid; InfzMEP-q-MVP Eseparation itmeets: 1allthe, requirementsf-so-f an acceptableasol. vents; good .solubility-and selectivity, low polymer" formation-and ease-.of recovery.y In addition-,tit not severely f corrosive@ Itis-an objective-ofthe present inventiomtoprovid an: improved 'process fory theVA recovery of'H organic ntrogenv. bases from liquidmixturesthereof; Anotherobjectzisther' recovery of hetero-cyclic nitrogenrcompounds fromiliquid mixtures thereo-f= by liquid-liquid extraction .employing 'za 1 carbonio acid; solution. l Awmore specific.Z obiectis-the:` sepa-ration.offMEPffromrMVPby a:lliquidliquidiextrac-, tion:emplo.yinga carbonic iacidrsolutioni `In its essentials, the present inventionacomprisesftreating. a .liquid streamf oontaininggseveral organic .nitrogenibasesrwithzan extractorfsolutionof Cog-.infwaten SinceaCOz andrwater, on one ,hand,.-.and.carbonic acid,. onsthetother," will `be .in equilibrinrm .the `ac-idity of-.ths 'solutionv may;;beincreasednby .dissolving 4more LCO2 '.in .theY water, as; for.- exampleby usingjhigher. pressures-to cause.more COzygtoi. A dissolve., Typical. 1of..=the separationacolurnns..suitable yfor,.-y liqnid-liquid .extraction .of this.. typetis.. that .described .in iv lthe Koch'patent, U. S.' 2,401,569. The-.feed streamentersw ice 'i such-anextractor columnat about its center,v water enters at the top; CO2 -is injectedinto they colurnnY several trays below the top rand some is generally premixed with thefeed. The water ows down through the column, extracting from/the feed the bulle, of the stronger nitrogen bases, which are more soluble inacarbom'c acid .than the weaker nitrogen bases. The latter rise through the downflowing carbonio acid column and are withdrawn `at the top of the column as raffinate. Water enteringat the top of the column serves both to absorb CO2 and to wash or extract CO2 from ythe rainate. lIn the typical case where MVP and MEP .are -thefnitrogen compounds-being separated, the solubility of MEPi'in water increases as the concentration of-'COz in the waterincreases, and vice versa. It is therefore desirable to have MEP presen-t when the carboni-c acid solution. is being prepared. The CO2 is introducedat'a'point below'the'point where the water enters" `and is absorbed. as it L moves countercurrently through1 thef'downilowing-water.' A heatv exchange means is provided to remove the heat of'solution of CO2 from fthesolvent stream. Also, cooler-absorber Vessels are providedin the feed and retlux streams to supply. the desired concentrationof CO2 and, at the same time, to cool them tothe temperature of theextractor column. The non- .aqueous raf'nate'and vthe aqueous extract are cooled. and depressurizedtorelease CO`2,therefrom, dewatered, and subjected to suitable separation' treatments. to recover MVP'and Ml-EP, respectively.

The separation of solvent from 'nitrogen' bases in' the extracts'easily made in'accordance withithis'invention. The invention," of course, pertains -only'to nitrogen bases which formaqueousrand non=aqueous 'phases with wat-er, theinvention being carried out under conditions such that one of the nitrogen bases is merel soluble thanl the yotlier'inaqueous solutions: 'Iii' addition, themore basic nitrogen `base'must be: atleast as water-soluble as tirelessk basi-c vcompound ('so' that solubilities andV :p H- values will -be'in the same-'directioni )Th'eedegree of basicity is a measure ofethe-ioniZationfconstant. Bynitrogen"bases I mean compounds-such?:1s-aliphatic `andA aromatic amines, quaternary ammonium-Z salts,l and"v heterocyclic nitrogen' compounds which may befconsidere'd 'organic substitution products off ammonia.-` -Byfaheterocyclic nitrogen compound 'Ii mean al1-compound.vll containinga heterocyclic nitrogenatom;y The'inventin-isf applicable'-orl the separ-ation not "vonlyl `of"aliphatic' and aromatic amines, octyl- =amine, =hexylamine'; minne-derivatives,-etci, but of pyridine derivatives,' quin-oline* derivatives, piperidine -fderivativesgl carbazole derivatives, and the like.

The invention is particulrlyrapplicable for the separationfofreadilypolymerizable compounds-:such aslmethylvinylpyridineffrom.rnethylethylpyridine v For. example, 2,-L methyl-.Sl-vinyl pyridine.(M-VP.) is.-.-p roduced..by catalytic dehydrogenati'on of--Z-methyl-.S-:ethyl.pyridine.(MEP) ac cording tothe following reaction:

Incaddition to the main product, MVP, a certainzamount of. pyridine, as such, 2picoline, 3-pic-oline,S-ethylpyridine; lutidine (2,5-dirnethyl pyridine.),.and. 3-.viny1--pyridineby-products are produced.

The vinylpyridines are useful intermediates inthe Iprep-f. aration of lfibers, adhesives, ion exchange resins, andy syn-z v.thetic rubber. The recovery of unreacted MEPand MVP" from .the dehydrogenation product poses a separation: problem which can be eiiciently handled -by the methodsl of the present invention.

Another specific example yof `the versatility -of-the^ present invention is the separation of VEP (2-vinyl-5-ethy-l pyridine) from MEP (Z-methyl-S-ethyl pyridine). VEP

is the equivalent of MVP in many respects and is prepared by reacting MEP with formaldehyde and dehydrating the lreaction product, according to the following reactions:

CHnCHQOH The product from the above dehydration reaction poses a separation problem similar to that of MVP-MEP separation in that in both cases the vinyl component polymerizes at elevated temperatures.

As indicated, CO2 dissolved in Water to form the solvent of this invention will form a ratiinate and an extract, each richer in their respective components than the feed on a solvent-free basis. Normally, sucient CO2 is dissolved in Water to ensure a desired solubility level, say sufficient so that at least twice as much of the mixture of nitrogen bases dissolves in the solution as would dissolve in the water in the absence of CO2. A convenient method of keeping sufficient CO2 in solution is to operate with water saturated, or almost saturated, under operating conditions which will depend primarily upon the extent of solubility of nitrogen bases to be separated, say a temperature of from 40 F. to 200 F. and a pressure of from 50 to 400 p. s. i. g.

The selectivity of the acid extraction is a function of the dissociation of the several nitrogen bases in the mixture. In the case of MEP-MVP mixtures, as presently understood, selectivity does not depend upon salt formation and it is believed that little salt formation occurs. While there may be some type of selective neutralization, any bonding to form salts must be very weak because it is broken by mere depressurizing.

This invention will be more readily understood by reference to the accompanying drawing, taken in conjunction with the example below. In the drawing, reference to the final details of product purication, by-product recovery, etc., have been omitted. Only suiicient equipment to illustrate the basic extraction process has been shown.

Example Referring to the drawing, the feedstock is admitted to the system through line 1 at the rate of 33,571 pounds/ stream day and at a temperature of 150 F. This stream has the following composition in terms of pounds per stream day:

Lbs./stream day Water 4,591 2-picoline 544 -picoline 512 4-picoline 21 2,5-dimethy1 pyridine 608 3-ethyl pyridine 320 3-vinyl pyridine 670 2-methyl-5-ethyl pyridine 18,960

This stream enters vessel 2, a combination cooler and CO2 absorber. Here the feedstock temperature is reduced to F. by indirect heat exchange with a suitable coolant, for example, water. At the same time, gaseous CO2 is injected into the feedstock through line 3 at the rate of 3950 pounds/stream day and is absorbed by the feedstock which is then introduced into extraction column 4 at about its center. Column 4 is a cylinder 51/2 in diameter and high with 55 inverted Koch trays. CO2 is injected into the column several trays below the top through line 5, a branch of line 39, at the rate of 39,856 pounds/stream day. Water, mostly recycle from a later step in the process and admixed with minor amounts of the components present in the feedstock, is admitted near the top of the column through line 49 at the rate of 919,085 pounds/stream day, of which said other components constitute 3315 pounds/stream day. The CO2 from line 5 bubbles up through the Water, dissolving therein to a large extent to form carbonio acid in situ which solution ows down through the column countercurrently to the feedstock admitted through line 1. The descending acid solution selectively dissolves the more basic component, MEP, as it contacts the feedstock and, hence, the extract withdrawn at the base of the column through line 10 is richer in MEP than was the feedstock. This extract is withdrawn at the rate of 1,019,200 pounds/stream day and contains 923,500 pounds of water and 43,800 pounds of MEP, the remainder being assorted pyridines and picolines present in the feedstock. The MVP in the feedstock, being less soluble in the descending carbonio acid than the MEP, rises countercurrently therethrough, emerging as rainate at the top of the column from which it is withdrawn throughvline 7. Water entering the top of the column through line 49 scrubs CO2 from the ratiinate stream and absorbs it, the CO21 migrating from the solution in which it is more highly concentrated to the solution of lower COz concentration. In addition the water unavoidably becomes saturated with MVP. To remove the heat of solution of CO2 in water, a side stream is constantly withdrawn from the upper portion of column 4, above the point of CO2 introduction, circulated through line 8 and heat exchanger 9, and returned to the column.

The extract withdrawn through 10 circulates throughextract heater 11 where it is heated from 95 F. to F., and is then admitted to flash separator 12, which is held under a pressure of 2 p. s. i. g. This combination of low pressure and high temperature flashes oif all but a trace of the CO2 from the extract, along with minor amounts of water and pyridine compounds. The CO2 is withdrawn overhead through line 13 and cooled from 150 F. to 90 F. in extract cooler 14; here over 80 percent of the moisture content and all but the last traces of the pyridine content of the CO2 collects. The substantially pure CO2 is withdrawn overhead from knockout drum 15 through line 16 and sent to line 37 for passage through compressor equipment, indicated generally at 38, preparatory to its recycle to column 4. The bottoms from ash separator 12 and knockout drum 15 are withdrawn through lines 17 and 18, respectively,l and pumped into phase separator 19, maintained at a ternperature of 150 F. and a pressure of 2 p. s. i. g. This is a duplication of the conditions in flash separator 12; substantially all of the CO2 remaining in the combined bottoms is tiashed olf and passed through line 20 to line 13 Where it combines with the overhead from ash separator 12. With the liberation of the CO2, the liquid separates into two phases. As indicated by the dotted line, a lower aqueous phase and an upper organic phase forms in 19. The upper phase consists of MEP admixed with minor amounts of water and other pyridines. Thisy phase is drawn oi through pipe 21, the top of which extends above the interface of the two phases, and divided into two approximately equal portions; one portion recycled as reux through line 22 and reux coolerabsorber 23:, described below, ,tothelowerportion .of column 4. The other portion is, suitably processed for concentration ofthe MEP andfrecoveryfoffbyproducts. The aqueousV phase from separator 19 "is withfy drawn through line 25`and passedV to a waterstripper 26. This is a tray column 42 x 30' maintained 'at a pressure of 2 p. s..i. g., a top-temperature-of210` F.,.;af;bottom temperature of 217 F., and equipped with a conventional reboiler. Thel overhead from-26; principally water and MEP, plus minorA amountsof lou/er.. pyridines and` picolines, is recycledA throughline 27. andszcondenser Zfto phase separatorll. Water. withdrawnflfrom the-base of 26 througho is,cooled at.29. and returned to column4, makeup'HZO being. added atfi9.

The ratlinate is withdrawnfrom column 4 atline 7. at 12,700 '-poundslstreamday; this..is. about 65 %`i MVP'L, 14% water, and8%..CO.2,..alL.intpartsfby weight;.tl1e remainder containsminoramounts ofrother pyridines rand heavy residues. This is. heated frlomfitsfiwithdrawal.temperature of 100 F. to a temperature of 150 F. in rafnate heater 30 and then introduced into a raffinate surge tank 31. This is maintained at a temperature of 150 F. and a pressure of 2 p. s. i. g.; the CO2 in the ranate is flashed olf and passed via line 32 through cooler 33, wherein it is cooled from 150 F. to 95 F., at which temperature it enters knockout drum 34. Here the pyridines entrained in the CO2 condense out and are returned through line 35 to raffinate surge tank 31, with the now substantially pure CO2 passing overhead through 36 into makeup-CO2 line 37. Line 37 conveys the combined CO2 streams to a three-stage compressor indicated generally at 3S. This compresses the CO2 successively to 34 p. s. i. g., 145 p. s, i. g., and 505 p. s. i. g. At the latter pressure it is returned through line 39 to the extraction system where it divides into three approximately equal streams; one-third through line to column 4, one-third through line 3 to feed cooler-absorber 2, and the remaining one-third to reux cooler-absorber 23. The latter is pressured to 500 p. s. i. g. and, by indirect heat exchange, cools reux stream 22 from 150 F. to 95 F. Under this combination of cooling and high pressure, reflux stream 22 becomes saturated with CO2 to substantially the same degree as the feedstock in Vessel 2, and both enter column 4 at the same temperature. Condensate from the intercoolers in compressor 38 passes through line 38a to extract phase separator 19. The condensate is principally water, but contains about MEP by weight and traces of other pyridines.

The liquid bottoms removed from 31 is about 75% MVP by weight and 12% water by weight, the remainder consists mainly of minor amounts of other pyridines. This stream passes through line 40 to a water removal column 41. This is a vertical cylinder 25 high and 30" in diameter filled to a height of with Raschig rings and equipped with a conventional reboiler. Column 41 operates at a top temperature of 135 F. and a top pres sure of 23 mm. mercury absolute. Dry MVP, admixed with minor amounts of MVP polymer, polymerization inhibitor, and other pyridines, is removed at the base of column 41 and sent to suitable purification apparatus for recovery of MVP and by-products. The overhead is withdrawn through line 42 and cooler 43 to accumulator 44 maintained at 95 F. and a pressure of 22 mm. of mercury absolute. This condenses out the MVP, along with minor amounts of other pyridines; this condensate is returned through line 45 to the top of raffinate surge tank 311. The overhead from 44 passes through line 46 to condenser 47; the water condensate is removed through line 38 and combined with the water in line 6.

A small amount of H2 and Ng is vented from column 4 through line S0, along with some CO2.

It is'believed apparent that the invention is not limited to the foregoing examples, these being but illustrative, and that various modifications can be made in the way of.temperatura,pressure,` equipment, etc., without departing from; the spirit of'fthe invention.V Thus while the: specific example showsv dividing. into two equalparts the:

phase drawn .oifthrough line 21,'.so thatione half goes back tothe extraction column. as, reflux, it should be made clear thatthis is merely., illustrative, not limiting.

The amount of reflux returned to a tray separator of theV the amountl of'lCOg admittedto. eaclrof the pointsis theV amount necessaryI to, saturate with1CO2 rthe solutions wi'n'ggpast 7saidpoints. Thus, if the. amount of reflux.` sent to absorber 23`is reduced 'by 50% from that recited.^

in the example, then the amount of CO2 admitted to 23 would be reduced 50%. While the make-up water is shown added at 49, it can be added at other points, also. For example, if a steam jet is used to pull the vacuum on accumulator 44, the steam could be condensed in 47 and thus added to the system.

I claim:

1. In a process for resolving -a mixture of heterocyclic nitrogen compounds in which a feed stock comprising an .aqueous solution of heterocyclic nitrogen compounds of varying basicity is introduced into the intermediate portion of a vertically elongated extraction zone, carbonic acid solution is allowed to descend through the feed stock whereby the more basic heterocyclic compounds in the feed sto-ck are selectively extracted by said acid, the resulting extract is washed with an upowing reflux stream obtained in a manner hereinafter described and the extract is withdrawn from the base of the extraction zone, a raffinate richer in the less basic heterocyclic nitrogen compounds on a solvent-free basis than the feed mixture is withdrawn from the upper portion of the extraction zone, carbon dioxide is liberated from the withdrawn raffinate and extract, the decarbonated extract is allowed to separate into an aqueous and an organic phase, a portion of the organic phase is withdrawn, said organic phase is substantially saturated with carbon dioxide and returned to the lower portion of the extraction` zone as reflux, the improvement which comprises saturating the feed stock with carbon dioxide, introducing a water stream into the upper portion of the extraction zone, introducing carbon dioxide into said zone between the feed stock stream and the water stream and absorbing carbon dioxide from the ascending rafnate in the water stream to form the carbonic acid employed in the liquid-liquid extraction.

2. The process of claim 1 wherein the remainder of the organic phase of the extract is dewatered and concentrated for recovery of the more basic heterocyclic compounds.

'3. The process of claim 1 wherein the rainate is de- Watered and concentrated for recovery of the less basic heterocyclic nitrogen compounds.

4. In a processfor the separation of methylvinylpyridine and methylethylpyridine from an aqueous solution there of in which said solution is introduced into an intermediate point of a vertical extraction zone, carbonic acid solution is flowed downwardly through the solution whereby the methylethylpyridine is selectively dissolved in said carbonic acid and removed as extract from the base of the extraction zone while the methylvinylpyridine rises through the extraction zone and is withdrawn near the top as raffinate, and methylethylpyridine is recovered from said extract and methylvinylpyridine is recovered from said raffinate, the improvement which comprises saturat- ,7 ing said solution with carbon dioxide, introducing water into the upper portion of the extraction zone, introducing carbon dioxide into the upper portion of said zone at a point between the entry of said solution and water streams and absorbing the carbon dioxide in the Water to form the carbonic acid employed in the extraction process.

5. The process of claim 4 comprising in addition, separating the water from the decarbonated water and extract, leaving a methylethylpyridine concentrate and a methylvinylpyridine concentrate, combining the Water into one stream and recycling it to the extraction zone.

6. The process of claim 4 comprising the additional steps of freeing the Withdrawn extract of carbon dioxide, allowing the decarbonated extract to separate into an aqueous phase and an organic phase consisting primarily of methylethylpyridine, dividing said organic phase into two portions, substantially completely saturating one portion with carbon dioxide and returning said saturated portion to the lower region of the extraction zone as reflux.

o 7. The process of claim 6 wherein the carbon dioxide liberated from the extract and ranate is compressed and divided into three streams, said streams being injected into the feed stock, the extraction zone and the reflux, respectively.

References Cited in the file of this patent UNITED STATES PATENTS 1,965,828 Fox July 10, 1934 2,082,034 Smith June 1, 1937 2,189,278 Bailey Feb. 6, 1940 2,288,281 Huijser June 30, 1942 2,486,778 Doumani Nov. 1, 1949 2,516,370 Cracas July 25, 1950 2,541,458 Berg Feb. 13, 1951 2,556,228 Sauders June l2, 1951 2,569,391 Stearns Sept. 25, 1951 2,755,282 Hachmuth July 17, 1956v 

1. IN A PROCESS FOR RESOLVING A MIXTURE OF HETEROCYCLIC NITROGEN COMPOUNDS IN WHICH A FEED STOCK COMPRISING AN AQUEOUS SOLUTION OF HETEROCYCLIC NITROGEN COMPOUNDS OF VARYING BASICITY IS INTRODUCED INTO THE INTERMEDIATE PORTION OF A VERTICALLY ELONGATED EXTRACTION ZONE, CARBONIC ACID SOLUTION IS ALLOWED TO DESCEND THROUGH THE FEED STOCK WHEREBY THE MORE BASIC HETEROCYCLIC COMPOUNDS IN THE FEED STOCK ARE SELECTIVELY EXTRACTED BY SAID ACID, THE RESULTING EXTRACT IS WASHED WITH AN UPFLOWING REFLUX STREAM OBTAINED IN A MANNER HEREINAFTER DESCRIBED AND THE EXTRACT IS WITHDRAWN FROM THE BASE OF THE EXTRACTION ZONE, A RAFFINATE RICHER IN THE LESS BASIC HETEROCYCLIC NITROGEN COMPOUNDS ON A SOLVENT-FREE BASIS THAN THE FEED MIXTURE IS WITHDRAWN FROM THE UPPER PORTION OF THE EXTRACTION ZONE, CARBON DIOXIDE IS LIBERATED FROM THE WITHDRAWN RAFFINATE AND EXTRACT, THE DECARBONATED EXTRACT IS ALLOWED TO SEPARATE INTO AN AQUEOUS AND AN ORGANIC PHASE, A PORTION OF THE ORGIC PHASE IS WITHDRAWN, SAID ORGANIC PHASE IS SUBSTANTIALLY SATRUATED WITH CARBON DIOXIDE AND RETURNED TO THE LOWER PORTION OF THE EXTRACTION ZONE AS REFLUX, THE IMPROVEMENT WHICH COMPRISES SATURATING THE FEED STOCK WITH CARBON DIOXIDE, INTRODUCING A WATER STREAM INTO THE UPPER PORTION OF THE EXTRACTION ZONE, INTRODUCING CARBON DIOXIDE INTO SAID ZONE BETWEEN THE FEED STOCK STREAM AND THE WATER STREAM AND ABSORBING CARBON DIOXIDE FROM THE ASCENDING RAFFINATE IN THE WATER STREAM TO FORM THE CARBONIC ACID EMPLOYED IN THE LIQUID-LIQUID EXTRACTION. 